CVE-2026-78426 in NeuVector
Summary
by MITRE • 09/17/2026
The NeuVector JWT verifier accepts noncanonical Base64URL encodings of the same RSA signature field. An attacker holding a valid JWT that has not expired, but was logged out of NeuVector, can continue using the non-expired token with equivalent spelling of the RSA signature field until the token validity expires.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability in question resides within the JSON Web Token verification logic implemented by NeuVector, specifically concerning how the system processes cryptographic signatures encoded in Base64URL format. JWTs are a compact, URL-safe means of representing claims to be transferred between two parties, and their security relies heavily on the integrity of the signature field which ensures that the token has not been tampered with since it was issued by the trusted identity provider. In this specific instance, the verifier exhibits an inconsistency in its parsing routine where it fails to strictly enforce canonical encoding standards for the Base64URL representation of the RSA signature. This technical flaw allows multiple distinct byte sequences to be interpreted as valid representations of the same underlying cryptographic value, effectively creating a scenario where syntactically different but semantically equivalent tokens are accepted by the authentication mechanism.
From an operational perspective, this lack of strict canonicalization creates a significant bypass for session management controls. When a user is logged out or their access rights are revoked in NeuVector, the system typically invalidates the associated JWT to prevent further use. However, because the verifier accepts noncanonical encodings of the signature field, an attacker who possesses a valid, unexpired token can manipulate its encoding without altering the actual cryptographic proof of authenticity. By simply changing the spelling or padding of the Base64URL string in the signature portion of the header or payload, the attacker presents a variant that passes verification checks despite being logically associated with a revoked session. This allows the malicious actor to maintain active access and execute commands within the NeuVector environment until the token's expiration time is reached, effectively nullifying immediate logout procedures designed to mitigate compromise.
The security implications of this flaw are severe as it directly undermines the principle of least privilege and timely revocation of access credentials. It falls under the category of CWE-20 Improper Input Validation, specifically relating to the failure to validate that input conforms to expected canonical forms before processing cryptographic operations. Furthermore, in the context of the MITRE ATT&CK framework, this behavior aligns with techniques related to Token Manipulation and Defense Evasion, as it allows an adversary to persist within a system by exploiting inconsistencies in how authentication tokens are validated against revocation lists or session states. The ability to reuse revoked credentials extends the window of opportunity for lateral movement, data exfiltration, or further exploitation of container orchestration vulnerabilities that NeuVector is designed to monitor and protect against.
To mitigate this vulnerability, it is imperative that developers enforce strict canonicalization rules when parsing JWT components. This involves ensuring that Base64URL encoded fields are decoded using a standard-compliant library that rejects noncanonical representations, such as those with incorrect padding or unnecessary whitespace variations that do not map to the exact same byte sequence expected by the signature verification algorithm. Implementing rigorous input validation checks that compare the canonical form of the token against stored session data can prevent this bypass. Additionally, NeuVector should implement short-lived tokens combined with robust refresh mechanisms and immediate invalidation upon logout events at a server-side level that does not rely solely on client-held token validity periods. Regular security audits focusing on cryptographic implementation details are essential to identify similar inconsistencies in other authentication flows within the platform.